From: Stefano Brivio <sbrivio@redhat.com>
To: David Ahern <dsahern@gmail.com>
Cc: Florian Westphal <fw@strlen.de>,
netdev@vger.kernel.org, aconole@redhat.com
Subject: Re: [PATCH net-next 1/3] udp_tunnel: allow to turn off path mtu discovery on encap sockets
Date: Sat, 18 Jul 2020 19:58:50 +0200 [thread overview]
Message-ID: <20200718195850.61104dd2@elisabeth> (raw)
In-Reply-To: <9e47f521-b3dc-f116-658b-d6897b0ddf20@gmail.com>
On Sat, 18 Jul 2020 11:02:46 -0600
David Ahern <dsahern@gmail.com> wrote:
> On 7/18/20 12:56 AM, Stefano Brivio wrote:
> > On Fri, 17 Jul 2020 09:04:51 -0600
> > David Ahern <dsahern@gmail.com> wrote:
> >
> >> On 7/17/20 6:27 AM, Stefano Brivio wrote:
> >>>>
> >>>>> Note that this doesn't work as it is because of a number of reasons
> >>>>> (skb doesn't have a dst, pkt_type is not PACKET_HOST), and perhaps we
> >>>>> shouldn't be using icmp_send(), but at a glance that looks simpler.
> >>>>
> >>>> Yes, it also requires that the bridge has IP connectivity
> >>>> to reach the inner ip, which might not be the case.
> >>>
> >>> If the VXLAN endpoint is a port of the bridge, that needs to be the
> >>> case, right? Otherwise the VXLAN endpoint can't be reached.
> >>>
> >>>>> Another slight preference I have towards this idea is that the only
> >>>>> known way we can break PMTU discovery right now is by using a bridge,
> >>>>> so fixing the problem there looks more future-proof than addressing any
> >>>>> kind of tunnel with this problem. I think FoU and GUE would hit the
> >>>>> same problem, I don't know about IP tunnels, sticking that selftest
> >>>>> snippet to whatever other test in pmtu.sh should tell.
> >>>>
> >>>> Every type of bridge port that needs to add additional header on egress
> >>>> has this problem in the bridge scenario once the peer of the IP tunnel
> >>>> signals a PMTU event.
> >>>
> >>> Yes :(
> >>
> >> The vxlan/tunnel device knows it is a bridge port, and it knows it is
> >> going to push a udp and ip{v6} header. So why not use that information
> >> in setting / updating the MTU? That's what I was getting at on Monday
> >> with my comment about lwtunnel_headroom equivalent.
> >
> > If I understand correctly, you're proposing something similar to my
> > earlier draft from:
> >
> > <20200713003813.01f2d5d3@elisabeth>
> > https://lore.kernel.org/netdev/20200713003813.01f2d5d3@elisabeth/
> >
> > the problem with it is that it wouldn't help: the MTU is already set to
> > the right value for both port and bridge in the case Florian originally
> > reported.
>
> I am definitely hand waving; I have not had time to create a setup
> showing the problem. Is there a reproducer using only namespaces?
And I'm laser pointing: check the bottom of that email ;)
--
Stefano
next prev parent reply other threads:[~2020-07-18 17:59 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-12 20:07 [PATCH net-next 0/3] vxlan, geneve: allow to turn off PMTU updates on encap socket Florian Westphal
2020-07-12 20:07 ` [PATCH net-next 1/3] udp_tunnel: allow to turn off path mtu discovery on encap sockets Florian Westphal
2020-07-12 22:38 ` Stefano Brivio
2020-07-13 8:04 ` Florian Westphal
2020-07-13 10:04 ` Stefano Brivio
2020-07-13 10:51 ` Numan Siddique
2020-07-14 20:38 ` Aaron Conole
2020-07-15 11:58 ` Stefano Brivio
2020-07-13 13:25 ` David Ahern
2020-07-13 14:02 ` Florian Westphal
2020-07-13 14:41 ` David Ahern
2020-07-13 14:59 ` Florian Westphal
2020-07-13 15:57 ` Stefano Brivio
2020-07-13 16:22 ` Florian Westphal
2020-07-14 12:33 ` Stefano Brivio
2020-07-14 12:33 ` Stefano Brivio
2020-07-15 12:42 ` Florian Westphal
2020-07-15 13:35 ` Stefano Brivio
2020-07-15 14:33 ` Florian Westphal
2020-07-17 12:27 ` Stefano Brivio
2020-07-17 15:04 ` David Ahern
2020-07-17 18:43 ` Florian Westphal
2020-07-18 6:56 ` Stefano Brivio
2020-07-18 17:02 ` David Ahern
2020-07-18 17:58 ` Stefano Brivio [this message]
2020-07-18 18:04 ` Stefano Brivio
2020-07-19 18:43 ` David Ahern
2020-07-19 21:49 ` Stefano Brivio
2020-07-20 3:19 ` David Ahern
2020-07-26 17:01 ` Stefano Brivio
2020-07-12 20:07 ` [PATCH net-next 2/3] vxlan: allow to disable path mtu learning on encap socket Florian Westphal
2020-07-16 19:33 ` Jakub Kicinski
2020-07-17 10:13 ` Florian Westphal
2020-07-12 20:07 ` [PATCH net-next 3/3] geneve: allow disabling of pmtu detection on encap sk Florian Westphal
2020-07-12 22:39 ` [PATCH net-next 0/3] vxlan, geneve: allow to turn off PMTU updates on encap socket Stefano Brivio
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